The present invention relates to a signal discriminator and a sync signal generator equipped with such a signal discriminator, and more particularly to those adapted to be applied to a high-density integrated circuit (IC).
It has been known in the related art heretofore that some video cameras or the like functionally have an internal sync mode to output a video signal produced in the individual device and an external sync mode to output a video signal synchronized with an external signal inputted from an external apparatus.
In a video camera of the type mentioned above, an internal sync mode is selected when the camera is operated individually, then a sync signal is generated in accordance with a signal produced in a sync signal generator incorporated therein, and a video signal synchronized with such a sync signal is outputted.
Meanwhile, when an alternating voltage signal of 60 Hz for example is inputted as an external signal from an AC power source of an external apparatus, there is selected a line lock mode which is one external sync mode, so that a sync signal synchronized in timing with the alternating voltage signal of 60 Hz is generated in the sync signal generator, and then a video signal synchronized with this sync signal is outputted.
Also when a monochrome video signal for example is inputted as an external signal from an external apparatus, there is selected a VS lock mode which is another external sync mode, where a sync signal synchronized with the monochrome video signal is generated in the sync signal generator, and then a video signal synchronized with this sync signal is outputted.
Further when a color video signal for example is inputted as an external signal from an external apparatus, there is selected a VBS lock mode which is still another external sync mode, where a sync signal synchronized with the color video signal is generated in the sync signal generator, and a video signal synchronized with this sync signal is outputted.
Generally the sync signal generator employed in the above-described video camera is formed into an IC, and exclusive input terminals are provided for respective kinds of external signals for producing sync signals.
With the recent technical progress achieved in enhancing the functions of apparatus, ICs are also developed in regard to the integration density, and remarkable increase is realized in the number of component circuits incorporated in each IC.
Consequently, there arises a great increase in the number of terminals required for the increased internal component circuits. However, since the number of terminals providable in each IC is limited, it follows that the number of input-output terminals of an interface is also restricted.
Accordingly, it has been demanded heretofore that, in the sync signal generator which is one of the component circuits incorporated in the IC, one of input terminals for a plurality of external signals fed from external apparatus is used in common to thereby reduce the number of input terminals allocated to the sync signal generator.